Catalyzed Chemical Synthesis of Unnatural Aromatic Polyhydroxyalkanoate and Aromatic–Aliphatic PHAs with Record-High Glass-Transition and Decomposition Temperatures

The catalyzed chemical synthesis of polyhydroxyalkanoates (PHAs) via stereoselective ring-opening polymerization (ROP) of eight-membered cyclic diolides (8DL R, R denotes the two substituents on the ring) has shown its ability to synthesize a variety of stereoregular aliphatic PHAs, but its utility for the synthesis of aromatic PHAs has not yet been demonstrated. Here, we report that the controlled ROP of meso -8DL Bn (Bn = benzyl)—catalyzed by metal-based complexes supported by C 2 -Salen ligands—affords syndiotactic ([ rr ] = 92%) poly(3-hydroxy-4-phenylbutyrate) ( st -P3H4PhB) with a high molar mass ( M n up to 147 kg mol –1 ) and the highest glass-transition temperature (43 °C) reported in the PHA family, whereas the ROP of rac -8DL Bn leads to essentially pure isotactic ([ mm ] > 99%) it -P3H4PhB. With judicious selections of catalysts, monomers, and procedures, copolymerizations of meso -8DL Bn with rac -8DL R (R = Me, n Bu) produces aromatic–aliphatic random, stereotapered, or crystalline stereo-diblock PHA copolymers. In particular, the copolymer of meso -8DL Bn with rac -8DL Bu —P3H4PhB- co -P3HHp ( M n = 205 kg mol –1 )—is a strong, hard, but ductile (∼191% elongation at break) material, displaying perhaps the highest decomposition temperature (281 °C) reported for PHAs to date.